Queue Delete at middle in constant time (Only possible way is using doubly linked list)

#include<bits/stdc++.h>
using namespace std;

struct doublyqueue {
int d;
doublyqueue* next=NULL;
doublyqueue* prev=NULL;
};
doublyqueue *front=NULL;
doublyqueue *rear=NULL;
doublyqueue *mid=NULL;
//  f->null r->null mid =null
// f->1<-r mid=1 i.e when changed from even to odd by push mid updated
// f->1>2><r mid =1 odd to ev no ch
//f->1>2>3<r mid=2 i.e mid=mid->next when changed to odd and n!=1
// f->1>2>3<r  deque 1 i.e,( changed from odd to even) then no change in mid
// f->2->3<r mid =2 deque again => only 1 ele and mid is 3 i.e mid=m->next if changed from even to odd 
// deque => mid= 2 i.e mid= mid->prev i.e

// now check for delete mid ex only  1 then mid=null
//if 1 2 mid=1 and delmid=> mid=m->next;
// if 1 2 3 mid= 2 del mid => mid=m->prev;
// 1 2 3 4 m=2 del 2 => 1 3 4 mid = 3 i.e m->next;
// i.e size reduced and if new size is odd => m=m->next
int size=0;
void push(int data)
{
// push in a queue => insertion at rear
doublyqueue *temp= new doublyqueue();
temp->d=data;
size++;

// base case if queue is empty
if(front==rear && !front)// front=r=NULL
{
front=temp;
rear=temp;
mid=temp;
}
else
{
// one element
rear->next=temp;
temp->prev=rear;
rear=temp;
if(size%2!=0)// changed from even to odd
{
mid=mid->next;
}

}
}
void  pop()
{
// delete at front
int d;

if(front==rear && !front) // if empty
{
mid=NULL;

return;
//return -1;
}
else if( front == rear)
{ size--;
d= front->d;
front=NULL;
rear=front;
mid=front;
}
else
{ size--;
d= front->d;
front=front->next;
front->prev=NULL;
if(size%2!=0)
{
mid=mid->next;
}
}
return;
//return d;
}
void displayfromfront(doublyqueue *f)
{
while(f!=NULL)
{
cout<<f->d<<" ";
f=f->next;
}
}
void printmiddata()
{
if(mid!=NULL)
cout<< mid->d<<endl;
else
cout<< -1<<endl;
}
void  printtopdata()
{
int i= front!=NULL ? front->d : -1;
cout<<i<<endl;
}
void deletemid()
{

if(front==rear && !front)
{
return ;
}
else if(front==rear)
{
size--;
front=NULL;
rear=NULL;
mid=NULL;

}
else
{
doublyqueue* p =mid->prev;
doublyqueue* f =mid->next;
p->next=p->next->next;
f->prev=p;
mid->prev=NULL;
mid->next=NULL;
if(size%2==0)
{
mid=p;
}
else
{
mid= f;
}
}
}

int main(){
   
    int n; // elements to push
    cin>>n;
    while(n--){
        int d;
        cin>>d;
         push(d);
    }
    int t; // quries
    cin>>t;
    while(t--){
       
        cin>>n;
        if(n==1){
            int x;
            cin>>x;
            push(x);
        }
        else if(n==2){
          pop();
        }
        else if(n==3){
           
deletemid();
        }
        else if(n==4){
             printtopdata();
        }
        else if(n==5){
        printmiddata();
        }
        else if(n==6)
        {
        displayfromfront(front);
}
    }
}